This invention relates to the field of thin film magnetic write transducer structures and methods of fabrication.
Magnetic storage media use increasingly narrower track widths to increase the amount of data that can be recorded per square inch. The decrease in track width results in a weaker residual magnetic flux that must be sensed by the read transducers during data recovery. To increase the residual magnetic flux, magnetic materials with high coercive values are used in the storage media. The narrow track widths and high coercive values place high demands on the write transducers to write the data in the magnetic storage media. Narrow track widths require tight control of the pole dimensions and shape, in particular, of the top pole in thin film magnetic write transducers. High coercive magnetic storage media require the write transducer to produce high magnetic flux densities at the pole tips. Such high magnetic flux densities often result in the saturation of common magnetic materials such as Permalloy (80:20 NiFe)
Two widely used methods of controlling pole width and pole sidewall profiles during wafer fabrication are electroplating and ion milling. Optically patterned photoresist layers produce well defined, steep sidewall profiles that make excellent electroplating templates. In an electroplating process, an electrically conductive seedlayer is deposited on the wafer before the photoresist. The photoresist is then deposited, exposed, and developed. Plating is then performed with the seedlayer carrying the plating current. After plating, the photoresist is stripped and a quick etch removes the unwanted areas of the seedlayer. A drawback to this process is that a plated pole tends to be softer than a vacuum deposited pole. This results in a shorter life span for thin film magnetic heads in tape applications where the poles are subject to pole tip recession (PTR).
An ion milling process or focused ion beam can be used to trim poles created by plating, vacuum deposition, or any other method. Trimming is typically performed with ions impacting the air bearing surface or tape bearing surface of the thin film magnetic write heads. As a result, the trimming must be performed after the wafer has been cut and the air or tape bearing surfaces have been polished. This requirement complicates the fabrication process since subsections of the original wafer must be handled individually during these trimming steps. This process also leaves cavities in the air or tape bearing surfaces that can create problems in both hard disk and tape applications. In the case of ion milling, two extra processing steps are required to trim the poles. One extra step is the formation of an ion milling mask that defines where the poles are trimmed. The second extra step is the removal of the mask after the ion milling is completed. The mask itself is etched during the ion milling and some of the mask material is redeposited on the exposed pole. This can result in a rough air/tape bearing surface that impacts normal operations. Ion milling for long periods of time also result in sidewall sloping that further complicates control over the final pole dimensions.
In the article xe2x80x9cA New Write Head Trimmed at Wafer Level by Focused Ion Beam,xe2x80x9d IEEE Transactions on Magnetics, Volume 34, No. 4, July 1998 by Koshikawa et al., a fabrication method is disclosed where the pole tips are trimmed at the wafer level. After the top poles are deposited and patterned, a focused ion beam is used to trim the top poles, the write gaps, and part of the bottom poles to the desired width and shape. Subsequent insulation depositions fill any voids created by the ion trimming. The result is a top pole sidewall that is approximately normal to the write gap layer at the air or tape bearing surface. The Koshikawa process, though, is time consuming as the ion beam must cut through the entire thickness of the top pole.
Different approaches have been taken in attempts to increase the saturation magnetization limit at the pole tips of thin film magnetic write heads. For example, U.S. Pat. No. 5,224,002 issued to Nakashima et al. on Jun. 29, 1993 discloses a thin film magnetic head where the top and/or bottom poles each consist of two layers of magnetic material. The outer magnetic layers (furthest from the write gap layer) of the poles are fabricated with conventional magnetic materials that have conventional saturation magnetization characteristic. Disposed between the outer magnetic layers and the write gap layer are inner layers composed of a high saturation magnetization material. These high saturation magnetization layers allow the thin film magnetic head to produce a high magnetic flux density immediately adjacent the write gap where it is the most influential during writing.
Another approach for increasing the magnetic flux density at the pole tips is disclosed in U.S. Pat. No. 4,589,042 issued to Anderson et al. on May 13, 1986. Anderson discloses a thin film magnetic head where the regions of the top and bottom poles between the pole tips and coil windings are made of a high saturation magnetization material. The region of the poles adjacent the coil windings are made of conventional magnetic materials. This configuration allows a higher magnetic flux density at the pole tips than if the poles were fabricated entirely using the conventional magnetic materials.
U.S. Pat. No. 4,610,935 issued to Kumasaka et al. on Sep. 9, 1986 discloses a magnetic film structure consisting of very thin alternating layers of two different magnetic materials laminated together to produce a magnetic film having a high saturation magnetic induction and a low coercive force. Layers of a nonmagnetic insulating material may be included in the structure to help minimize eddy currents in thick films.
These various methods of increasing the saturation magnetization focus mainly on the magnetic flux at the pole tips. The Kumasaka disclosure also discusses the difficulties associated with the top pole layer transitioning between the thin write gap layer and the thicker coil insulating layer. Changes in the topology of the top pole can result in variations in the thickness and thus the magnetic properties. Kumasaka discloses that the multiple layers of the laminated film maintain the film""s magnetic properties through the steps in the topology. An assumption is made that the thickness of the laminated film is the same on flat regions as on sloped regions. This assumption is not always true when the top pole material is deposited by vacuum deposition or other methods involving a laminar deposition.
The present invention is a method of fabricating a thin film magnetic write transducer, and the resulting write transducer structure. The fabrication method involves deposition and patterning of a bottom pole, a write gap layer, a coil and a coil insulating layer. In subsequent steps, the method forms a top pole having two layers of magnetic material. A thin inner layer of high saturation magnetization material is disposed at wafer level after the coil insulating layer has been formed. Next, a photoresist layer is deposited and patterned above the top pole inner layer. A top pole outer layer is plated over the top pole inner layer using the photoresist layer as a plating mask. Plating is a quick and inexpensive method of building up the desired thickness of the top pole. After plating of the top pole outer layer has been completed and the photoresist has been stripped, the top pole inner layer is ion milled using the top pole outer layer as a mask. An advantage of this process is that only the thin top pole inner layer needs to be ion milled instead of the entire top pole thickness. This process provides good control of the top pole""s dimensions and results in a steep sidewall profile suitable for writing narrow data tracks in a magnetic storage media. By using a high saturation magnetization material for the top pole inner layer, the write transducer can produce a high magnetic flux density required to write in high coercive magnetic storage media. The rate at which the pole tips erode in magnetic tape applications is slowed when a hard magnetic material is used as the top pole inner layer.
In alternative embodiments, the bottom pole of the write transducer may also be fabricated in two layers. First, a bottom pole outer layer is formed on the substrate or undercoat layer. Next, a bottom pole inner layer is deposited to cover the bottom pole outer layer. A protective photoresist etch hat is formed to protect the desired regions of the bottom pole inner layer. The unwanted regions of the bottom pole inner layer are then removed using ion milling, wet chemical etching or other suitable process. Finally, the protective photoresist etch hat is removed. As with the top pole inner layer, using a high saturation magnetization material for the bottom pole inner layer increases the magnetic flux density that the write transducer is capable of producing. Using a hard magnetic material for the bottom pole inner layer slows the pole tip recission rate in magnetic tape applications.
Accordingly, it is an object of the present invention to provide a method for fabricating a thin film magnetic write transducer where the top pole is fabricated in two layers, a top pole inner layer adjacent to the write gap and a top pole outer layer, and where the top pole inner layer is patterned using the top pole outer layer as a mask.
Another object of the present invention is to provide a method for fabricating a thin film magnetic write transducer that provides good control over the dimensions of the top pole at the media bearing surface, and produces approximately parallel sidewalls in the top pole.
Another object of the present invention is to provide a method for fabricating the bottom pole in two layers.
Yet another object of the present invention is to provide a thin film magnetic write transducer structure produced by the above processes.
These and other objects, features and advantages will be readily apparent upon consideration of the following detailed description in conjunction with the accompanying drawings.